The al-Hakim Mosque was built between 928 and 992 by Gawhar Al-Siqilli in the 10th century and was named after Imam Al-Hakim bi-Amr Allah. Over the years its been used as a prison by the Crusaders, a stable for Saladin, a fortress for Napoleon, and as a local school. During the 1980's the mosque was practically rebuilt with white marble, getting rid of its gravel flooring.
Links
http://www.touregypt.net/featurestories/hakimmosque.htm
http://en.wikipedia.org/wiki/Al-Hakim_Mosque